1. Field of the Invention
This invention relates to magnetic bubble domains, and more particularly to gapless propagation structures for implementing the controlled movement of magnetic bubble domains in a supporting medium.
2. Description of the Prior Art
In the new and rapidly developing field of technology relating to magnetic bubble domains the preferred means for implementing the controlled movement of bubbles within a magnetic medium, such as a platelet of orthoferrite or garnet material, has involved the use of overlay strips of permalloy or the like. These strips are magnetically soft, are laid down on top of the platelet, and serve to channel and concentrate the flux from a rotating in-plane magnetic field. This concentration produces poles at the ends of the strips when they are aligned with the rotating field, and these poles attract (or repel) the bubbles to thereby control their movement.
The permalloy structures currently in use include the T-I bar, Y-I bar, Y-Y bar and chevron patterns, and rely on gaps between the bars to provide a continuous flow of bubbles around the structures in the presence of a rotating or pulse-sequenced magnetic field.
These gapped permalloy patterns are characterized by a number of major disadvantages. For one, the bubble diameter must be substantially larger (typically 2 times larger) than the gap width in order to traverse it. This reduces the density of storage which can be achieved for a given line width because unwanted magnetic interactions between bubbles require that bubbles be separated by distances greater than kD, where D is the bubble diameter and k is a device sensitive parameter, typically about 4. In addition, a bubble must be elevated to a higher energy state to traverse a gap, which renders it momentarily less stable and thus more likely to collapse, split, or otherwise behave in an erratic manner, thus reducing device operating margins. Finally, the close dimensional tolerances that must be maintained at the gaps makes the fabrication of the permalloy overlays more difficult and increases the likelihood of serious propagation errors occurring at the gaps.
Several propagation structures which are generally of a gapless form have been proposed in the prior art, as typified by U.S. Pat. Nos. 3,516,077 (tangent discs on alternately opposite sides of a platelet), U.S. Pat. No. 3,518,643 (zig-zag strip), and U.S. Pat. No. 3,644,908 (sinuous strip alongside a straight strip). All of these structures have a number of disadvantages, however, such as low packing density and the ability to implement bubble movement in only a single direction.
It is therefore an object of the present invention to provide singlesided, gapless propagation structures for implementing the controlled movement of magnetic bubble domains in a supporting medium.
It is a further object of the invention to provide such structures of the closed loop type wherein bubbles may be propagated in any direction for any given drive field sequence, including the simultaneous propagation of a plurality of bubbles in different and even opposite directions in response to the same drive field.